Sinking a 990 m surface borehole for methane drainage of a longwall panel in a UK coal mine

Methane drainage is employed in gassy coal mines to capture sufficient of the methane produced to maintain an atmosphere that is within legal limits. Traditionally, in the UK this has been by a network of underground boreholes drilled above the waste from the return gate. In early 2005, one already gassy colliery experienced a major methane emission from the waste that caused production to be suspended. This paper describes the event and the effects it had, details the work done to control the situation, then shows how the decision was taken to drill the UK's first 'gob well' as a longer term solution. With the workings lying at a depth of 987 m, oil well technology had to be employed. Water-bearing strata was passed through and the paper presents the procedures put into place to ensure the safety of the mine and its personnel as the borehole thirled with the waste.